Mystery illness kills scores of lamprey

Environment Southland is investigating the death of hundreds of kanakana, or lamprey, in the lower Mataura River in recent weeks.

Environment Southland aquatic scientist Andy Hicks yesterday confirmed kanakana in the lower Mataura River appear to be affected by an unknown illness. The alarm was raised about two weeks ago but samples were only able to be collected this week.

They have been sent to MAF to test for pathogens and the council hoped to have the results in a couple of weeks, he said.

With the much anticipated opening of the fishing season today, Southland Fish and Game is assuring fishermen there is no cause for the concern.

Senior officer Zane Moss said the density of trout in the Mataura River was as high as it had ever been, and whatever was affecting the lamprey was unlikely to affect the trout. The Mataura River remained one of the most popular trout fisheries in the country, he said.

Mr Hicks said the kanakana appeared to have red coloured fins and red contusions on their bodies. The illness appeared to be widespread in the migrating population.

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"We don't know what has caused these contusions; it could be a pathogen, it could be related to contaminants in the water, it could be that the contusions are from scrapes or other predators."

There had been no obvious changes in the river conditions or predator numbers, he said.

Hokonui runanga kaiwhakahaere Rewi Anglem, who oversees management of the Mataura River mataitai, was among the first to notice the problem. It was a major concern, he said this week.

Mr Anglem estimates about 90 per cent of kanakana running in the Mataura River were affected by the illness. However, there were no reports of kanakana in the Waikawa River, another major harvesting area, being struck by it. "It seems quite strange."

The kanakana were a customary food source but Mr Anglem said he would not be eating any until the cause of the illness was known.

Mr Hicks said the public should not eat kanakana that did not appear completely healthy.

Environment Southland was keen to test more samples to see how widespread the illness was and whether it had affected other species. People should put the sample in a plastic bag, wrap it in paper, chill or ice it, and "give us a call". The samples should not be frozen, he said.

Last month Nigel Murch raised concerns on the Southland Times Facebook page, after discovering dead and dying lamprey less than a metre from the river's edge.

WHAT ARE LAMPREY

The lamprey (Maori name kanakana) spends most of its life in the sea but spawns in fresh water. They are parasites, sustaining themselves at sea by latching on to whales and large fish and sucking their blood and juices.

The adults do not feed while in fresh water, so are not parasitic on other freshwater fish. Lamprey can be distinguished from eels by the presence of the circular sucker instead of a mouth and seven holes along their sides just behind the head.

They are common in Southland in the Mataura and Waikawa rivers, swimming upstream to spawn from around August to the end of October. Sources: Environment Southland and NIWA websites